1. Field of the Invention
This invention relates to conveyor systems and more particularly to a magnetic conveyor system.
2. Description of the Prior Art
Envelope machines which transform cut paper blanks into finished envelopes require conveyor systems for transporting the envelope blanks from one portion of the machine to another. These conveyor systems must be capable of gripping the blank and holding it in proper alignment during the transport thereof. In addition, the longest conveyor reaches extends from the feeder section of the machine which generally includes an adhesive applying section for applying the closure flap adhesive, through a dryer section to an envelope forming section. Due to the necessity of thoroughly drying the closure flap adhesive before allowing that adhesive to come into contact with other surfaces, the transport from the adhesive applying section is along a relatively long path. However, during transport, it is necessary that the blank be firmly gripped to be carried along at the full machine speed while at the same time maintaining alignment of the blanks with respect to the machine.
Such transport has normally been carried out through the use of endless chain conveyors which either have gripping members which individually grip the paper or are biased into firm pressure engagement with one another with the paper entrapped therebetween. Such chains are extremely expensive while at the same time being subject to wear and breakage. When a given length of the chain has worn and is in need of replacement, it is a time intensive task to replace the link. Additionally, when the link is replaced, the resultant chain, due to looseness between other links, may have a different overall length than initially. More importantly, since the paper is usually gripped by two chains, one on each side of the paper so as to leave the adhesive applied flap free of contact, it is possible that the chains will achieve different lengths. Since the links of the chain will not be consistent, but will vary throughout the entire length of the chain due to looseness or tightness between adjacent links and the tensions applied thereto, it is possible for different sections of the chains to be moving at different relative speeds sufficient to misalign the blanks between the parallel running chains.
Of course should one of the links break before replacement, the maintenance task of repairing and replacing that chain is quite complicated. In addition, such chains are extremely heavy and require undesirably large energy expenditures to move them.
While other transport devices, such as driven rollers and the like have been used, the necessity of firmly gripping each blank and of maintaining it in alignment without contacting the gummed area of the blank has required that such alternative transport devices be extremely complex and expensive.
Although it is known to use magnetism in connection with transport devices, such uses have either relied upon use of electromagnets to energize ferrous armatures which will move conveyor bllt backing plates (see for example U.S. Pat. No. 3,227,344 to Rutter) or they have involved the use of permanent magnets mounted on a surface for attracting and holding on the surface metallic members, (see for example U.S. Pat. No. 2,958,019 to Scholten). It has also been known to utilize electromagnets disposed underneath a conveyor to attract metallic objects to be carried into contact with the conveyor surface (see U.S. Pat. No. 3,199,654 to Buccicone). In addition, it has been known to impart an electrostatic charge to a sheet of paper to cause the paper to adhere to a specially constructed conveyor tape (see U.S. Pat. No. 3,761,074 to Benbenek). Each of the prior art magnetic force utilizing transport systems has particular advantages and disadvantages. Among the disadvantages are the inability to transport non-magnetic devices or non-charged devices in those systems which utilize either permanent magnet coatings to the conveying surface or magnetic underlayments or electrostatic chargers. Particularly, devices which rely upon applying an electrostatic charge to the paper are undersirable in high speed machinery because of the difficulty of totally eliminating the electrostatic charge at the desired point. Once the charge has been applied to moving paper, that charge has a tendency to remain with the paper and will cause the paper to move improperly through other parts of the machinery and will further cause the paper to adhere to similar charged papers.
However, a chief advantage of the use of magnetism in transporting devices is the ability to eliminate heretofore complex mechanical grasping means or the prior used opposed weight devices or other types of pressure applying constructions.
It would therefore be an advance in the art to provide a magnetic transport system for moving non-metallic sheets wherein the magnetic force is utilized to hold the sheets in place in the conveyor system without applying a charge to the sheets.